Hi Rajender Saini,
Welcome to Microsoft Community.
As you mentioned, the fluctuation issue you are experiencing occurs after modifying the monitor frequency.
This is not a software-level problem.
The change in the parameters of the hardware output signal, combined with frequencies that are recognizable to the human eye, allows you to observe the change.
The resolution of the display is not exactly one-to-one with the frequency, and its support modes are limited.
For your Display2, if you want to modify its resolution, make sure it supports the corresponding resolution/frequency combination.
- Go to Settings >> Display. Click Advanced Settings and scroll down to the very bottom of the advanced settings screen. Click Display adapter properties.
- This will open the properties for the display adapter. In the Adapter tab, click the List all modes button. This will open a new window listing every single resolution that your display can support. Select it here and click OK followed by Apply on the properties window.
The current possible feasible recommendation is to try resetting the refresh rate.
Given that you mentioned that there is no such option in the drop-down menu.
So, it seems that one possible way is to try to uninstall and reinstall the driver for the corresponding display.
Update drivers manually in Windows - Microsoft Support
This is not guaranteed to work, and if you cannot revert to the default refresh rate, it is recommended to consult the instruction manual for your device or consider contacting the hardware manufacturer.
If there is anything not clear, please do not hesitate to let me know.
Best Regards,
Kyo - MSFT | Microsoft Community Support Specialist